Modern motor vehicles are often already fitted with an electronically controlled damping system as standard by which the damping behavior of controllable vibration dampers (for example wheel-guiding suspension struts) on the wheel suspensions can be controlled. More precisely, a controlled damping system of this type usually comprises three sensors fitted on the vehicle body which are able to detect a speed of the vehicle body, assumed as being a rigid plate, relative to the chassis in a perpendicular (vertical) direction to the surface of the roadway. Furthermore, the vibration dampers are each provided with sensors which can detect a (vertical) upwards and downwards movement or corresponding speeds of the vehicle wheels. The various sensors transmit the detected speed data to an open-and closed-loop control unit of the damping system, which open-and closed-loop control unit for its part is actively connected to actuators of the controllable vibration dampers. In the open-and closed-loop control unit, vertical movements or speeds of the vehicle body relative to the chassis are compared with vertical speeds of the wheels on the wheel suspensions on the basis of the speed data from the sensors, the speeds emerging from the respective differences during the compression/recoil of the vibration dampers. A control value for the actuators of the vibration dampers is then determined from this data using a program map and is transmitted to the actuators, as a result of which a desirable damping behavior of the vibration dampers on the wheel suspensions can be obtained. In order to achieve a control of the damping system which is adapted as effectively as possible to the respective driving situation, further sensors are provided for the most part to detect the vehicle speed, the vehicle lateral acceleration (for example using a steering angle sensor) and the variation in the vehicle lateral acceleration (for example using a step steering input sensor).
The aim of every controlled vehicle damping system is to influence in a desirable manner the vibration behavior of a motor vehicle, i.e. the manner in which the vehicle body moves with respect to the chassis when induced by the road (unevenness of the road). In this respect, a movement is generally desired in which the front axle and the rear axle of the vehicle are deflected outwards as far as possible in an identical manner with the same amplitude and come to rest again as far as possible at the same time, so that the vehicle body as such makes no pitching or rolling movements, or as few pitching or rolling movements as possible.
However, a disadvantage of conventional damping systems in vehicles is that a varying payload of the vehicle has only a very restricted influence on the speed, detected in conventional damping systems, of the vehicle body relative to the chassis. In this respect, hitherto it has only been possible to coordinate an inhibition of pitching and rolling movements of the vehicle body within the program map control with one specific reference condition, namely either for an empty vehicle or a vehicle for which a certain loading with persons and/or loaded freight is assumed. For this reason, conventional damping systems in vehicles have hitherto not afforded any possibility of considering different loading conditions of the vehicle which, however, can occur very often in the practical use of the vehicle, or any possibility of optimizing an inhibition of vibrations of the vehicle body under different loading conditions.
Thus, it is also known from practice that in the case of large vehicle payloads beyond a payload assumed for the vehicle reference condition of the program map control, a permanent underdamping of the vibration dampers, in particular of the rear axle of the vehicle can occur due to a load acting in a non-uniform manner on the axles, which permanent underdamping disadvantageously results in pitching movements of the vehicle body which can only be damped to a limited extent by the electronic damping system and, moreover, entail a relatively great expense in terms of control. Basically, a vibration damper cannot completely avoid movements, since only the movement itself produces a damping effect. This problem of a payload loading the axles in a non-uniform manner is accentuated in vehicles with a relatively low service weight, as in this case the payload has a greater effect compared to a vehicle which is heavier per se.
Pitching movements cannot, however, be completely avoided, as the front axle and the rear axle always pass over an obstacle in a delayed manner. (In practice, a certain remainder of pitching movements is allowed anyway, because too strong a compensation results in an uncomfortable “jarring”, vibration behavior and rolling). Payload increases this ever present “residual pitching motion”, resulting in an uncomfortable driving behavior. If the payload restricted by the manufacturer is exceeded, the driving behavior can even become uncontrollable.
Accordingly, an object of the present invention is to provide a method for the axle load-dependent or loading-dependent control of an electronically controlled damping system in a vehicle, and to provide a damping system of this type, with which it is possible to optimize, for different loadings of the vehicle, an inhibition/damping of vibrations, in particular pitch vibrations of the vehicle body which are caused in particular by a load stressing the axles non-uniformly.